"All You Need is Love" by The Beatles is played as Number Six is taken to the council chamber and during the climactic shoot-out. Other music featured is "Dem Bones" by The Four Lads (during Forty-Eight's trial and on the A20), and "I Like You Very Much" by Carmen Miranda (as Rover melts).
The area rubbed clean on the blackboard by Number Two changes size and shape between the close up of him and the board and the wide shot of Number Six, the butler and Number Two.
This episode strongly suggests that Number Six (Patrick McGoohan) served as a fighter pilot in World War II. His date of birth was revealed as March 19, 1928 in "Arrival" which means that if he entered the RAF as a recruit at the minumum permitted age of 17, he would have been able to serve for less than six months before the war ended.
Number Two's pennyfarthing on his badge faces to the left and to the right during different shots of the same scene.
At about 16 minutes into 'Once Upon A Time', Number Two is seen writing on a black board. As the camera shot goes from long to closeup, the printing on the black board changes. The most noticeable difference is the "F" in find.
When Number Six believes that he has been poisoned, he consumes a number of different alcoholic beverages to induce vomiting so he can get rid of the poison. The drinks, in order, are: brandy, whiskey, vodka, Drambuie, Tia Maria, Countreau, and Grand Marnier.
This is the only episode of The Prisoner to feature children living in the Village.
In the cellar fight, Nigel Stock's hair changes from ginger to gray and becomes substantially longer and bushier when the stunt man is substituted.
Approximately 30 minutes into 'Do Not Forsake Me Oh My Darling' the rebodied Number Six walks into a Photographic Shop. On the door an advertisement poster is folded over twice at the top so as not to show the product name. A moment later Number Six looks back through the door and sees a man watching - the poster is now only folded once and advertises "The Polaroid Swinger".
In some of the car driving shots the actor is not Nigel Stock but looks to be McGoohan. This is particularly evident after he has left the camera shop and is returning back home, as the car makes a right hand turn. Likely due to using stock footage of McGoohan driving rather than filming Nigel Stock doing it.
After his first meeting with Number Six, Number Two leaves the flat, and twenty seconds later he's back in the Green Dome watching Number Six finishing his conversation with Eighty-Six.
John Sharp is credited by his alias "John Sharpe" in the credits.
Goof: In 'A Change Of Mind' after approximately 9 minutes have passed and as Number Six walks up a bricked walkway, you can see a white car pass in the background at the end of the walkway.
It's rather odd why Number 6 wasn't immediately detained after leaving the "bomb" on Number 2's doorstep, especially granted his past "suspicious" behaviour that involved cuckoo clocks in It's Your Funeral, which preceded this episode when shown in proper viewing rather than production order.
Number Seventy-Three (Hilary Dwyer) is the only use of the numeral "7" seen in the Village.
In the first 15 minutes there is a point where Number 6 looks in a shop window. Just before he goes in to listen to records there is a blue sign and a yellow sign displayed in the window. They switch sides from left to right between camera cuts.
At the trial, the Observer says she saw Number Six on the bell tower with the radio with Number Two present. The earlier scene took place on an open overlook above the beach, not in the bell tower.
At approximately the 26:10 mark, as Number Six runs through the woods on his way to the beach, the stand-in is clearly not Patrick McGoohan: he has much longer hair and lacks McGoohan's receding hairline.
As Number Six's return to Britain, which occurred on March 18, took approximately 30 days, he would have escaped from the Village on or around February 23.